When a voltage source is connected to an inductor and a switch and if the switch has been closed for a period of time, a positive potential on the voltage source drives a current through the inductor, such that it becomes fully or substantially fully energized. A second terminal of a voltage source is coupled to a first terminal of the inductor and a first terminal of the switch is coupled to a second terminal of the inductor. A second terminal of the switch and a first terminal of the voltage source are connected to ground.
When the switch is opened, the fully or substantially fully energized inductor attempts to resist a sudden drop in current by using its magnetic field energy to create its own voltage and supply current, through the switch. As a result, an extremely large increase in the positive potential is created at the second terminal of the inductor. The switch, being connected between the second terminal of the inductor and ground, has to withstand this high potential difference. Since no connection is physically made to allow current to continue to flow (due to the switch being open), this large potential difference can cause electrons to “arc” between the terminals of of the open switch. This behavior can cause rise in temperature inside the switch and may burn the switch. Similarly, for non-mechanical solid state switches (e.g. a transistor), large voltage drops across the terminals of an open solid state switch can destroy the component in question either instantaneously or through accelerated wear and tear.